JP6131821B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  Conventionally, an internal combustion engine is known in which a NOx adsorbent for adsorbing NOx in exhaust gas and a NOx purification catalyst for purifying NOx in exhaust gas are arranged in an engine exhaust passage. In this internal combustion engine, from the start of engine operation until the temperature of the NOx purification catalyst reaches the activation temperature, NOx in the exhaust gas is adsorbed by the NOx adsorbent, and thus NOx is prevented from being released into the atmosphere. The

  However, the gas present in the engine exhaust passage while the engine is stopped contains moisture, and this moisture is adsorbed by the NOx adsorbent before the engine is restarted. As a result, the amount of NOx that can be adsorbed by the NOx adsorbent when the engine is restarted is reduced by the amount of moisture adsorbed by the NOx adsorbent. That is, the amount of NOx released into the atmosphere before the temperature of the NOx purification catalyst reaches the activation temperature may increase by the amount of moisture adsorbed on the NOx adsorbent.

  Therefore, an electric heater is attached to the NOx adsorbent, the amount of water adsorbed on the NOx adsorbent is calculated, and when the adsorbed water amount exceeds the threshold amount, the electric heater is operated to raise the temperature of the NOx adsorbent. An internal combustion engine is known in which moisture is released from the NOx adsorbent (see Patent Document 1).

JP 2002-155736 A

  However, in Patent Document 1, the moisture release action is not performed until the amount of adsorbed moisture reaches the threshold amount. As a result, the amount of NOx that can be adsorbed by the NOx adsorbent is reduced by the amount of water adsorbed by the NOx adsorbent, apart from immediately after the moisture releasing action is performed. Therefore, there is still a possibility that the amount of NOx released into the atmosphere before the temperature of the NOx purification catalyst reaches the activation temperature increases. Alternatively, it is necessary to increase the adsorption capacity of the NOx adsorbent by the amount of moisture to be adsorbed.

  According to the present invention, the NOx adsorbent for adsorbing NOx in the exhaust gas and the NOx purification catalyst for purifying NOx in the exhaust gas are arranged in the engine exhaust passage, and the NOx adsorbent is NOx When the temperature of the NOx adsorbent reaches the moisture desorption temperature when the temperature of the adsorbent is increased, the adsorbed water begins to desorb, and when the temperature of the NOx adsorbent is further increased, the temperature of the NOx adsorbent is increased. When the NOx adsorbing temperature is reached, the adsorbed NOx has a property of starting to desorb, and an electric heater for raising the temperature of the NOx adsorbent is provided. An exhaust purification device for an internal combustion engine that starts supplying power to the electric heater before the explosion completes and supplies the electric heater with an amount of power that causes the temperature of the NOx adsorbent to be higher than the moisture release temperature and lower than the NOx release temperature. Offer It is.

  While maintaining the adsorption capacity of the NOx adsorbent small, it is possible to suppress the release of NOx into the atmosphere until the temperature of the NOx purification catalyst reaches the activation temperature.

1 is an overall view of an internal combustion engine. It is a front view of a particulate filter. It is side surface sectional drawing of a particulate filter. It is a partial expanded sectional view of the partition of a particulate filter. It is a diagram explaining a moisture desorption temperature and a NOx desorption temperature. It is a diagram explaining the activation temperature of a NOx purification catalyst. It is a time chart explaining the electric heater control of the Example by this invention. It is a figure which shows the map of the amount of initial adsorption moisture QAW0. It is a flowchart which shows an electric heater control routine. It is a time chart explaining the electric heater control of another Example by this invention. It is a time chart explaining the electric heater control of another Example by this invention. It is a flowchart which shows the electric heater control routine of another Example by this invention. 7 is a flowchart showing another exhaust gas purification control routine for NOx adsorbent.

  Referring to FIG. 1, 1 is a main body of a compression ignition type internal combustion engine, 2 is a combustion chamber of each cylinder, 3 is an electromagnetically controlled fuel injection valve for injecting fuel into the combustion chamber 2, and 4 is an intake manifold, Reference numeral 5 denotes an exhaust manifold. The intake manifold 4 is connected to the outlet of the compressor 7 c of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 c is sequentially connected to the air flow meter 9 and the air cleaner 10 via the intake introduction pipe 8. An electrically controlled throttle valve 11 is disposed in the intake duct 6, and a cooling device 12 for cooling intake air flowing through the intake duct 6 is disposed around the intake duct 6. On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 t of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 t is connected to the exhaust aftertreatment device 20.

  Each fuel injection valve 3 is connected to a common rail 14 via a fuel supply pipe 13, and this common rail 14 is connected to a fuel tank 16 via an electrically controlled fuel pump 15 having a variable discharge amount. The fuel in the fuel tank 16 is supplied into the common rail 14 by the fuel pump 15, and the fuel supplied into the common rail 14 is supplied to the fuel injection valve 3 through each fuel supply pipe 13. In the embodiment shown in FIG. 1, this fuel is composed of light oil. In another embodiment, the internal combustion engine comprises a spark ignition internal combustion engine in which combustion is performed under a lean air-fuel ratio. In this case, the fuel is composed of gasoline.

  The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 17, and an electrically controlled EGR control valve 18 is disposed in the EGR passage 17. A cooling device 19 for cooling the EGR gas flowing in the EGR passage 17 is disposed around the EGR passage 17.

  The exhaust aftertreatment device 20 includes an exhaust pipe 21 connected to an outlet of the exhaust turbine 7t. The exhaust pipe 21 is connected to an exhaust pipe 23 through a casing 22. A particulate filter 24 for collecting particulate matter in the exhaust gas is disposed in the casing 22, and a NOx adsorbent 25 for adsorbing NOx in the exhaust gas on the particulate filter 24, A NOx purification catalyst 26 for purifying NOx in the exhaust gas is supported. In addition, an electric heater 27 is disposed integrally with the particulate filter 24 in the casing 22 upstream of the particulate filter 24. Further, the exhaust pipe 21 located upstream of the NOx purification catalyst 26 is provided with a reducing agent supply valve 28 for supplying a reducing agent into the exhaust gas.

  The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, an input port 35 and an output port 36. It comprises. A temperature sensor 8T for detecting the temperature of air in the intake air introduction pipe 8 is attached to the intake air introduction pipe 8, and a temperature sensor 25T for detecting the temperature of the NOx adsorbent 25 is attached to the NOx adsorbent 25. . In the example shown in FIG. 1, the temperature of the NOx adsorbent 25 represents the temperature of the particulate filter 24 and the NOx purification catalyst 26. The output voltages of the air flow meter 9 and the temperature sensors 8T and 25T are input to the input port 35 via the corresponding AD converters 37, respectively. A load sensor 40 that generates an output voltage proportional to the amount of depression of the accelerator pedal 39 is connected to the accelerator pedal 39, and the output voltage of the load sensor 40 is input to the input port 35 via the corresponding AD converter 37. The Further, a crank angle sensor 41 that generates an output pulse every time the crankshaft rotates, for example, 30 degrees is connected to the input port 35. The CPU 34 calculates the engine speed based on the output pulse from the crank angle sensor 41. A signal indicating whether the ignition switch 42 operated by the vehicle driver is on or off is input to the input port 35. On the other hand, the output port 36 is connected to the fuel injection valve 3, the drive device for the throttle valve 11, the fuel pump 15, the EGR control valve 18, the electric heater 27, and the reducing agent supply valve 28 via corresponding drive circuits 38.

  2A and 2B show the structure of the wall flow type particulate filter 24. FIG. 2A shows a front view of the particulate filter 24, and FIG. 2B shows a side sectional view of the particulate filter 24. As shown in FIG. As shown in FIGS. 2A and 2B, the particulate filter 24 has a honeycomb structure, and a plurality of exhaust flow passages 71i and 71o extending in parallel with each other, and a partition wall separating the exhaust flow passages 71i and 71o from each other. 72. In the embodiment shown in FIG. 2A, the exhaust flow passages 71i and 71o are composed of an exhaust gas inflow passage 71i having an upstream end opened and a downstream end closed by a plug 73d, and an upstream end closed by a plug 73u and a downstream end. The exhaust gas outflow passage 71o is opened. In FIG. 2A, hatched portions indicate plugs 73u. Therefore, the exhaust gas inflow passages 71 i and the exhaust gas outflow passages 71 o are alternately arranged via the thin partition walls 72. In other words, in the exhaust gas inflow passage 71i and the exhaust gas outflow passage 71o, each exhaust gas inflow passage 71i is surrounded by four exhaust gas outflow passages 71o, and each exhaust gas outflow passage 71o is surrounded by four exhaust gas inflow passages 71i. Arranged so that. In another embodiment, the exhaust flow passage is constituted by an exhaust gas inflow passage whose upstream end and downstream end are opened, and an exhaust gas outflow passage whose upstream end is closed by a plug and whose downstream end is opened.

The partition wall 72 is formed of a porous material, for example, a ceramic such as cordierite, silicon carbide, silicon nitride, zirconia, titania, alumina, silica, mullite, lithium aluminum silicate, zirconium phosphate. Therefore, as shown by an arrow in FIG. 2B, the exhaust gas first flows into the exhaust gas inflow passage 71i, and then flows into the adjacent exhaust gas outflow passage 71o through the surrounding partition wall 72. Thus, the partition 72 constitutes the inner peripheral surface of the exhaust gas inflow passage 71i. In another embodiment, the partition wall or substrate is a porous resistance heating material, for example, a metal heating element such as a Ni—Cr alloy, molybdenum disilicide (MoSi ₂ ), or a non-metallic heating element such as silicon carbide (SiC). Formed from the body. In this case, the NOx adsorbent 25 is heated by energizing the partition wall, so that the partition wall acts as an electric heater 27.

  FIG. 3 shows a partially enlarged sectional view of the partition wall 72. As shown in FIG. 3, a layer of NOx adsorbent 25 is formed on the side surface of partition wall 72 on the exhaust gas inflow passage 71 i side, and a layer of NOx purification catalyst 26 is formed on the layer of NOx adsorbent 25. The

  In an embodiment according to the present invention, the NOx adsorbent 25 includes zeolite. In another embodiment, the NOx adsorbent 25 includes manganese Mn.

  When the temperature of the NOx adsorbent 25 is low, NOx is adsorbed by the NOx adsorbent 25, and when the temperature of the NOx adsorbent 25 becomes high, the adsorbed NOx is released from the NOx adsorbent 25 and released. Similarly, moisture is adsorbed on the NOx adsorbent 25 and desorbed from the NOx adsorbent 25.

  FIG. 4 shows the amount of moisture QDW and the amount of NOx QDN desorbed from the NOx adsorbent 25. As can be seen from FIG. 4, when the temperature TNA of the NOx adsorbent 25 is lower than the moisture desorption temperature TDW, the desorption moisture amount QDW is maintained almost zero, and therefore, almost no moisture is desorbed from the NOx adsorbent 25. If the temperature TNA of the NOx adsorbent 25 reaches the moisture desorption temperature TDW when the temperature TNA of the NOx adsorbent 25 is increased, the desorbed water amount QDW increases from zero, and therefore the moisture adsorbed on the NOx adsorbent 25. Begins to leave. On the other hand, when the temperature TNA of the NOx adsorbent 25 is lower than the NOx desorption temperature TDN, the desorbed NOx amount QDN is maintained almost zero, and therefore NOx is hardly desorbed from the NOx adsorbent 25. When the temperature TNA of the NOx adsorbent 25 is further increased and the temperature TNA of the NOx adsorbent 25 reaches the NOx desorption temperature TDN, the desorbed NOx amount QDN increases from zero and is therefore adsorbed by the NOx adsorbent 25. NOx begins to leave. In the embodiment according to the present invention, the moisture desorption temperature TDW is about 100 ° C., and the NOx desorption temperature TDN is about 180 ° C., which is higher than the water desorption temperature TDW.

On the other hand, in the embodiment according to the present invention, the NOx purification catalyst 26 is composed of a NOx selective reduction catalyst suitable for reducing NOx in the exhaust gas with a reducing agent under an excess of oxygen. This NOx selective reduction catalyst contains titania TiO ₂ as a carrier, vanadium oxide V ₂ O ₅ supported on this carrier, or zeolite ZSM5 as a carrier, and contains copper Cu supported on this carrier. Further, a urea aqueous solution is supplied from the reducing agent supply valve 28, and ammonia generated from the urea aqueous solution acts as a reducing agent. In another embodiment, fuel (hydrocarbon) is used as the reducing agent.

  If the ratio of the air and fuel (hydrocarbon) supplied into the engine intake passage, the combustion chamber 2 and the exhaust passage upstream of the NOx purification catalyst 26 is referred to as the air-fuel ratio of the exhaust gas, in another embodiment, the NOx purification catalyst 26 Is composed of a NOx storage catalyst that stores NOx contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and releases the stored NOx when the air-fuel ratio of the inflowing exhaust gas becomes rich. This NOx storage catalyst includes noble metal catalysts such as platinum Pt, rhodium Rh and palladium Pd, alkali metals such as potassium K, sodium Na and cesium Cs, alkaline earth metals such as barium Ba and calcium Ca, and lanthanoids. And a basic layer containing at least one selected from metals capable of donating electrons to NOx, such as rare earth and silver Ag, copper Cu, iron Fe, and iridium Ir. The term occlusion includes adsorption and absorption.

  FIG. 5 shows the relationship between the NOx purification rate EFF of the NOx purification catalyst 26 and the temperature TC of the NOx purification catalyst 26. As shown in FIG. 5, the NOx purification rate EFF of the NOx purification catalyst 26 increases as the temperature TC of the NOx purification catalyst 26 increases and reaches a peak. In this case, if the temperature TC of the NOx purification catalyst 26 is equal to or higher than the activation temperature TCACT, the NOx purification rate EFF becomes equal to or higher than the allowable value EFF1. In the embodiment according to the present invention, the activation temperature TCACT of the NOx purification catalyst 26 is set to about 180 ° C. which is substantially equal to the NOx removal temperature TDN of the NOx adsorbent 25. In another embodiment, the activation temperature TCACT of the NOx purification catalyst 26 is set lower than the NOx removal temperature TDN of NOx.

  Now, when the operation of the internal combustion engine is started, the exhaust gas is guided to the particulate filter 24. In this case, even if the temperature of the NOx purification catalyst 26 is lower than the activation temperature TCACT, NOx is adsorbed by the NOx adsorbent 25. As a result, NOx is suppressed from being discharged into the atmosphere. Next, the temperatures of the NOx adsorbent 25 and the NOx purification catalyst 26 are raised by the exhaust gas. When the temperature of the NOx adsorbent 25 reaches the NOx desorption temperature TDN, NOx adsorbed from the NOx adsorbent 25 starts to desorb, and the desorbed NOx flows into the NOx purification catalyst 26. At this time, the temperature TC of the NOx purification catalyst 26 has reached the activation temperature TCACT, and therefore NOx is purified by the NOx purification catalyst 26. When the temperature TC of the NOx purification catalyst 26 reaches the activation temperature TCACT, the supply of the reducing agent from the reducing agent supply valve 28 is started.

  By the way, if moisture is adsorbed to the NOx adsorbent 25 when the operation of the internal combustion engine is started, the amount of NOx that can be adsorbed by the NOx adsorbent 25 is reduced by this amount of moisture. On the other hand, if the temperature TNA of the NOx adsorbent 25 is increased to the moisture desorption temperature TDW, the moisture can be desorbed from the NOx adsorbent 25.

  Therefore, in the embodiment according to the present invention, when a signal indicating the start request of the internal combustion engine is issued, the power supply to the electric heater 27 is started before the internal combustion engine is completely exploded, and the temperature TNA of the NOx adsorbent 25 is started. Is supplied to the electric heater 27 with an amount of power that becomes equal to or higher than the moisture release temperature TDW and lower than the NOx release temperature TDN. As a result, the temperature of the NOx adsorbent 25 can be increased before the exhaust gas flows into the NOx adsorbent 25. Further, since the temperature TNA of the NOx adsorbent 25 is set to be equal to or higher than the moisture desorption temperature TDW and lower than the NOx desorption temperature TDN, the moisture can be desorbed from the NOx adsorbent 25 while the NOx adsorbent 25 is adsorbed. Therefore, the amount of NOx that can be adsorbed by the NOx adsorbent 25 can be increased. Therefore, it is possible to further suppress the release of NOx into the atmosphere until the temperature TC of the NOx purification catalyst 26 reaches the activation temperature TCACT while keeping the adsorption capacity of the NOx adsorbent 25 small.

  In the embodiment according to the present invention, the signal indicating the start request of the internal combustion engine is composed of a signal indicating that the ignition switch 42 is ON. In another embodiment, the internal combustion engine is started from a signal indicating that the starter motor switch is on, a signal indicating that the vehicle door has been opened, or a signal indicating that the vehicle door has been unlocked. A signal representing the request is constructed. In yet another embodiment, in a hybrid vehicle that includes an electric motor and an internal combustion engine and the internal combustion engine is operated when the vehicle driving force should be increased or the battery charge amount should be increased, a request for increasing the vehicle driving force is made. The signal indicating the start request of the internal combustion engine is configured from the signal indicating or the signal indicating the increase request of the battery storage amount.

  As described above, when the electric power is supplied to the electric heater 27, moisture is released from the NOx adsorbent 25. In the embodiment according to the present invention, it is determined whether or not the amount of adsorbed moisture of the NOx adsorbent 25 is smaller than the threshold amount during the power supply to the electric heater 27. When it is not determined that the amount of moisture adsorbed by the NOx adsorbent 25 is less than the threshold amount, power supply to the electric heater 27 is continued. When it is determined that the amount of moisture adsorbed by the NOx adsorbent 25 is less than the threshold amount, the power supply to the electric heater 27 is stopped. As a result, it is possible to prevent excessive electric power from being supplied to the electric heater 27.

Next, an embodiment according to the present invention will be further described with reference to FIG.
Referring to FIG. 6, time ta1 indicates the timing when the ignition switch 42 is turned on. In the example shown in FIG. 6, the adsorbed moisture amount QAW of the NOx adsorbent 25 at the time ta1 is the initial amount QAW0. When the ignition switch 42 is turned on at time ta1, supply of electric power to the electric heater 27 is started. That is, the electric heater 27 is activated. As a result, the temperature TNA of the NOx adsorbent 25 increases. Further, the amount of power EEH supplied to the electric heater 27 starts to increase.

  Next, when the temperature TNA of the NOx adsorbent 25 reaches the moisture desorption temperature TDW at time ta2, the moisture adsorbed from the NOx adsorbent 25 begins to desorb. As a result, the adsorbed moisture amount QAW of the NOx adsorbent 25 starts to decrease. In this case, electric power is supplied to the electric heater 27 so that the temperature TNA of the NOx adsorbent 25 is equal to or higher than the moisture release temperature TDW and lower than the NOx release temperature TDN. As a result, moisture is released from the NOx adsorbent 25 while NOx is adsorbed on the NOx adsorbent 25.

  Next, when the power amount EEH supplied to the NOx adsorbent 25 reaches the required power amount EEHR at time ta3, the power supply to the electric heater 27 is stopped. This required power amount EEHR is an amount of power required to reduce the amount of adsorbed moisture QAW of the NOx adsorbent 25 from the initial amount QAW0 to a threshold amount QAWT. Therefore, when the power amount EEH supplied to the NOx adsorbent 25 reaches the required power amount EEHR, it can be determined that the adsorbed water amount QAW of the NOx adsorbent 25 is smaller than the threshold amount QAWT. In the example shown in FIG. 6, the adsorbed moisture amount QAW of the NOx adsorbent 25 is smaller than the threshold amount QAWT at time ta3. The threshold value QAWT is set to almost zero in the example shown in FIG.

  Roughly speaking, the required power amount EEHR is the amount of power required to raise the temperature TNA of the NOx adsorbent 25 to the moisture desorption temperature TDW and the amount of water (QAW0-QAWT) from the NOx adsorbent 25 is desorbed. It is expressed as a total with the amount of power required. The former can be obtained in advance according to the heat capacity of the NOx adsorbent 25, more precisely, according to the heat capacities of the NOx adsorbent 25, the NOx purification catalyst 26, and the particulate filter 24 in the example shown in FIG. On the other hand, the latter is determined according to the amount of water adsorbed by the NOx adsorbent 25 when the power supply to the electric heater 27 is started, that is, the above-mentioned initial amount QAW0. As shown in FIG. 7, the initial adsorption moisture amount QAW0 increases as the atmospheric temperature TA when the supply of electric power to the electric heater 27 is started decreases. The initial adsorbed moisture amount QAW0 is stored in advance in the ROM 32 as a function of the atmospheric temperature TA in the form of a map shown in FIG. It should be noted that the atmospheric temperature TA when power supply to the electric heater 27 is started is detected by the temperature sensor 8T (FIG. 1).

  In FIG. 6, X indicates the timing at which the operation of the internal combustion engine is started, and Y indicates the timing at which the internal combustion engine has completed a complete explosion, that is, the timing at which the engine speed Ne exceeds a predetermined set speed NeC. ing. In the embodiment shown in FIG. 6, the supply of electric power to the electric heater 27 is started before the timing Y when the internal combustion engine completes explosion (ta1). Therefore, the temperature of the NOx adsorbent 25 can be quickly increased. Further, in the embodiment shown in FIG. 6, after the supply of electric power to the electric heater 27 is stopped (ta3), the engine operation is started (X), and the internal combustion engine is completely exploded (Y). Therefore, before the exhaust gas from the internal combustion engine flows into the NOx adsorbent 25, the amount of NOx that can be adsorbed by the NOx adsorbent 25 can be increased in advance. In another embodiment, power supply to the electric heater 27 is started (ta1), engine operation is then started (X), power supply to the electric heater 27 is then stopped (ta3), and then the internal combustion engine is completed. Explode (Y). In yet another embodiment, power supply to the electric heater 27 is started (ta1), engine operation is then started (X), the internal combustion engine is completely detonated (Y), and then electric power is supplied to the electric heater 27. Is stopped (ta3).

FIG. 8 shows a routine for executing the electric heater control of the embodiment according to the present invention. This routine is performed only once when the ignition switch 42 is turned on.
Referring to FIG. 8, in step 100, the atmospheric temperature TA is read. In the subsequent step 101, the initial adsorbed moisture amount QAW0 is calculated from the map of FIG. In the subsequent step 102, the required power amount EEHR is calculated. In the subsequent step 103, power supply to the electric heater 27 is started. In the subsequent step 104, the amount of power EEH supplied to the electric heater 27 is calculated. In the following step 105, it is determined whether or not the electric energy EEH supplied to the electric heater 27 is equal to or greater than the required electric energy EEHR. When EEH <EEHR, the process returns to step 103 and the power supply to the electric heater 27 is continued. When EEH ≧ EEHR, the routine proceeds to step 106 where the power supply to the electric heater 27 is stopped.

Next, another embodiment according to the present invention will be described with reference to FIG.
Referring to FIG. 9, power supply to the electric heater 27 is started at time tb1. In this case, the power supply to the electric heater 27 is controlled so that the temperature TNA of the NOx adsorbent 25 becomes the first target temperature TTNA1. Therefore, the temperature TNA of the NOx adsorbent 25 gradually increases. Next, when the temperature TNA of the NOx adsorbent 25 reaches the first target temperature TTNA1 at time tb2, the electric power supplied to the electric heater 27 is set so that the temperature TNA of the NOx adsorbent 25 becomes the second target temperature TTNA2. Increased in steps. As a result, the temperature TNA of the NOx adsorbent 25 increases.

  Next, when the temperature TNA of the NOx adsorbent 25 reaches the second target temperature TTNA2 at time tb3, it is necessary for the temperature TNA of the NOx adsorbent 25 to rise from the first target temperature TTNA1 to the second target temperature TTNA2. The calculated time dt (= tb3-tb2) is calculated. This required time dt represents the rate of increase in the temperature TNA of the NOx adsorbent 25 when the power supplied to the electric heater 27 is increased stepwise.

  This required time dt becomes shorter as the amount of moisture adsorbed on the NOx adsorbent 25 decreases. FIG. 9 shows a case where the amount of adsorbed moisture QAW of the NOx adsorbent 25 is small and therefore the required time dt is short. On the other hand, FIG. 10 shows a case where the amount of adsorbed moisture QAW of the NOx adsorbent 25 is large and therefore the required time dt is long.

  Therefore, in another embodiment according to the present invention, it is determined whether or not the required time dt is shorter than a predetermined set time dtS. When the required time dt is shorter than the set time dtS, the amount of adsorbed moisture of the NOx adsorbent 25 is determined. It is determined that the QAW has become smaller than the threshold amount QAWT, and the power supply to the electric heater 27 is stopped. As a result, excessive power supply to the electric heater 27 is prevented.

  When the required time dt is longer than a predetermined set time dtS, power supply to the electric heater 27 is continued. In this case, the power supply to the electric heater 27 is controlled so that the temperature TNA of the NOx adsorbent 25 becomes the first target temperature TTNA1. Next, when the temperature TNA of the NOx adsorbent 25 decreases to the first target temperature TTNA1, the electric power supplied to the electric heater 27 is increased stepwise again, and the required time dt is calculated again. Next, it is determined again whether or not the predetermined time dt is shorter than the set time dtS.

  That is, in another embodiment according to the present invention, the rising speed of the temperature TNA of the NOx adsorbent 25 when the electric power supplied to the electric heater 27 is increased stepwise is detected, and the rising speed is set to a predetermined value. When the speed is higher than the speed, it is determined that the amount of adsorbed water QAW of the NOx adsorbent 25 is smaller than the threshold amount QAWT.

  The first target temperature TTNA1 and the second target temperature TTNA2 are set between the moisture desorption temperature TDW and the NOx desorption temperature TDN. In another embodiment according to the invention, the first target temperature TTNA1 is set to 110 ° C. and the second target temperature TTNA2 is set to 120 ° C.

FIG. 11 shows a routine for executing the electric heater control of the embodiment according to the present invention. This routine is performed only once when the ignition switch 42 is turned on.
Referring to FIG. 11, in step 200, the electric heater 27 is activated. In the subsequent step 201, the target temperature TTNA of the NOx adsorbent 25 is set to the first target temperature TTNA1. As a result, the power supply to the electric heater 27 is controlled so that the temperature TNA of the NOx adsorbent 25 becomes the first target temperature TTNA1. In the following step 202, it is determined whether or not the temperature TNA of the NOx adsorbent 25 has reached the first target temperature TTNA1. When TNA ≠ TTNA1, the process returns to step 201. When TNA = TTNA1, the routine proceeds to step 203 where the target temperature TTNA of the NOx adsorbent 25 is set to the second target temperature TTNA2. In the next step 204, it is determined whether or not the temperature TNA of the NOx adsorbent 25 has reached the second target temperature TTNA2. When TNA ≠ TTNA2, the process returns to step 203. When TNA = TTNA2, the routine proceeds to step 205 where the required time dt is calculated. In the next step 206, it is determined whether or not the required time dt is shorter than a predetermined set time dtS. When dt ≧ dtS, the process returns to step 201. That is, power supply to the electric heater 27 is continued. When dt <dtS, the routine proceeds to step 207 where the power supply to the electric heater 27 is stopped.

  As described with reference to FIG. 3, in the embodiment shown in FIG. 1, the NOx adsorbent 25 and the NOx purification catalyst 26 are supported on a common base material, and the NOx adsorbent 25 is the base material. The NOx purification catalyst 26 is disposed on the side far from the base material, and the base material is composed of the particulate filter 24. In this way, not only the temperature of the NOx adsorbent 25 but also the temperatures of the particulate filter 24 and the NOx purification catalyst 26 can be quickly raised by the electric heater 27. Further, the volume of the casing 22 can be reduced.

  FIG. 12 shows another embodiment of the NOx adsorbent 25. In this embodiment, the NOx adsorbent 25 and the NOx purification catalyst 26 are supported on separate substrates, and the NOx adsorbent 25 is on the exhaust flow upstream side and the NOx purification catalyst 26 is on the exhaust gas flow downstream side. , Respectively. In this case, the base material carrying the NOx adsorbent 25 has a honeycomb structure and includes a plurality of exhaust gas flow passages separated from each other by thin partition walls. These exhaust gas flow passages are open at the upstream end and the downstream end. The NOx adsorbent 25 is supported on both side surfaces of each partition wall. This base material is configured in the same manner as the particulate filter 24. On the other hand, the base material carrying the NOx purification catalyst 26 is composed of the particulate filter 24. The electric heater 27 is attached to the NOx adsorbent 25, and the reducing agent supply valve 28 is disposed between the NOx adsorbent 25 and the NOx purification catalyst 26.

  In the example shown in FIG. 12, the particulate filter 24 is arranged downstream of the NOx adsorbent 25. As a result, the exhaust gas that has passed through the NOx adsorbent 25 heated by the electric heater 27 flows into the particulate filter 24, so that the temperatures of the particulate filter 24 and the NOx purification catalyst 26 are quickly raised.

  When expressed so as to include the embodiment shown in FIG. 1 and the embodiment shown in FIG. 12, the NOx adsorbent 25 and the NOx purification catalyst 26 so that NOx released from the NOx adsorbent 25 flows into the NOx purification catalyst 26. Is disposed in the engine exhaust passage.

1 Engine Body 21 Exhaust Pipe 24 Particulate Filter 25 NOx Adsorbent 26 NOx Purification Catalyst 27 Electric Heater 42 Ignition Switch

Claims (9)

A NOx adsorbent for adsorbing NOx in the exhaust gas and a NOx purification catalyst for purifying NOx in the exhaust gas are arranged in the engine exhaust passage, and the NOx adsorbent increases the temperature of the NOx adsorbent. When the NOx adsorbent temperature reaches the moisture desorption temperature, the adsorbed moisture begins to desorb, and when the NOx adsorbent temperature is further increased, the NOx adsorbent temperature reaches the NOx desorption temperature. The adsorbed NOx has the property of starting to desorb, and is equipped with an electric heater for raising the temperature of the NOx adsorbent. When a signal indicating a request for starting the internal combustion engine is issued, and starts power supply to the electric heater, and supplying the amount of power which the temperature is less than the water leaving temperature higher NOx leaving the temperature of the NOx adsorbent to the electric heater, and an exhaust purification device for an internal combustion engine, NOx adsorption Leaving the NOx is disposed NOx adsorbent and the NOx purification catalyst to flow into the NOx purifying catalyst from the exhaust purification system of an internal combustion engine.   When it is determined whether or not the amount of adsorbed moisture of the NOx adsorbent is smaller than the threshold amount during power supply to the electric heater, and it is determined that the amount of adsorbed moisture of the NOx adsorbent is smaller than the threshold amount The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein power supply to the electric heater is stopped.   When the amount of electric power required to reduce the amount of adsorbed moisture of the NOx adsorbent to be less than the threshold amount is obtained and the amount of electric power supplied to the electric heater reaches the required amount of electric power, the adsorbed moisture of the NOx adsorbent The exhaust emission control device for an internal combustion engine according to claim 2, wherein it is determined that the amount is less than a threshold amount.   The exhaust emission control device for an internal combustion engine according to claim 3, wherein the required amount of electric power is obtained based on an atmospheric temperature when electric power supply to the electric heater is started.   The NOx adsorbent temperature rise rate is detected when the electric power supplied to the electric heater is increased stepwise, and the adsorbed moisture amount of the NOx adsorbent when the rise rate is higher than a predetermined set speed. The exhaust emission control device for an internal combustion engine according to claim 2, wherein the exhaust gas purification device is determined to be less than a threshold amount. The NOx adsorbent and the NOx purification catalyst are supported on a common base material, and the NOx adsorbent is disposed on the side closer to the base material and the NOx purification catalyst is disposed on the side farther from the base material. 2. An exhaust emission control device for an internal combustion engine according to 1 . The exhaust purification device for an internal combustion engine according to claim 6 , wherein the base material is constituted by a partition wall of a particulate filter for collecting particulate matter in the exhaust gas. A NOx adsorbent and the NOx purifying catalyst are supported on one another separate substrate, the NOx adsorbent exhaust stream upstream, NOx purifying catalyst in the exhaust gas stream downstream, are arranged respectively, according to claim 1 2. An exhaust gas purification apparatus for an internal combustion engine according to 1. The exhaust emission control device for an internal combustion engine according to claim 8 , wherein a particulate filter for collecting particulate matter in the exhaust gas is disposed downstream of the NOx adsorbent.

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